Thanks for sharing your experience.
But...
Under the Common law system, which applies to the UK, Canada, Australia, etc, you have committed fraudulent misrepresentation, that you knowingly used a false statement of fact(evidence is shown in the macrumor forum) to induce the apple genius guy, who genuinely relied on your statement, into contract to replacing your 1.6 motherboard with a 1.8 one (Derry v Peek). Alternatively, statutory claim i.e. Misrepresentation Act 1967 s 2(1) can be relied on by Apple to make a claim as well. It is a breach of tort law and remedy including litigation cost can be sought by Apple Inc. I recommend you get a lawyer soon.